In modern DWDM systems, it is essential to have devices that can add and drop signals to and from a stream of signals. In U.S. Pat. No. 6,101,300, a bus waveguide and a drop waveguide are coupled to a resonator-system. At the resonant frequency of the resonator-system, a desired signal can be completely transferred from the bus waveguide to the drop waveguide. Higher order filters are realized by increasing the number of resonators. U.S. Pat. No. 6,101,300 also describes various switching mechanisms for providing on/off switching and modulation.